Relationship between electricity, magnetism, and relativity

[hideelo]

I know that magnetism can be explained as the relativistic interaction between say a current, and a moving charge. My question however is twofold, is magnetism nothing but electric forces when relativity is taken into account? If the answer is yes, does that make magnetism a sort of psuedo-force?

 

[mfb]

My question however is twofold, is magnetism nothing but electric forces when relativity is taken into account?

As long as there are no magnetic monopoles, I think you can see it in this way, but you don't have to. That's probably a philosophic question.

If there are magnetic monopoles (and we just did not find them so far), this is certainly not true.

If the answer is yes, does that make magnetism a sort of psuedo-force?

No.

 

[Naty1]

If the answer is yes, does that make magnetism a sort of psuedo-force?

not as ficticous forces are generally defined...

http://en.wikipedia.org/wiki/Pseudo_force


and there is a nice abbreviated description of electromagnmetism-SR here:

http://en.wikipedia.org/wiki/Magnetism#Magnetism.2C_electricity.2C_and_special_relativity

Follow the link at the top of this section for the full article...with details...

 

[Dale]

does that make magnetism a sort of psuedo-force?

The electromagnetic force is a real force. You can split the real electromagnetic force into an electric component and a magnetic component. These are components of a real force, not independent forces in their own right. Thus they are not pseudo forces, but they are frame dependent.

 

[hideelo]

Thanks to everyone for responding. Just to clarify, this is not two separate forces, not one force and a psuedo force, but one force seen from two different frames of reference?

 

[WannabeNewton]

Thanks to everyone for responding. Just to clarify, this is not two separate forces, not one force and a psuedo force, but one force seen from two different frames of reference?

Yes. There is one and only one electromagnetic field, which is a covariant object, and the Lorentz force law can be written in terms of the electromagnetic field. In order to split the electromagnetic field and the Lorentz force law into electric and magnetic components you must choose an inertial frame and the split depends on the choice of frame. I can go into the mathematical details if you wish.

 

[thegreenlaser]

I don't think relativity necessarily implies that you should see electric phenomena as more "fundamental" than magnetic phenomena. Rather, it seems to show that while an "electromagnetic" effect is definitely real, it doesn't make much sense to say that something is fundamentally "electric" or "magnetic" because that distinction is observer-dependent. So I would think that "electromagnetism" is the fundamental thing because even though not everyone agrees on whether something is "electric" or "magnetic," they can all agree that it's electromagnetic.

Note that in the mathematical formulation of relativistic electromagnetics, there's no preference given to the electric field over the magnetic field. The more important object is the electromagnetic field tensor, which includes both the electric and magnetic field.

 

[Dale]

Just to clarify, this is not two separate forces, not one force and a psuedo force, but one force seen from two different frames of reference?

Yes. Perhaps you recall doing inclined plane problems where you would break the force of gravity into a normal component and a sliding component. The one force is gravity, the normal and sliding forces are just components of that one force. How you split gravity up into normal and sliding forces depends on the angle of your "frame". It is a similar concept about how you split the EM force into E and M components.

 

[Naty1]

Here is an interesting perspective:

http://en.wikipedia.org/wiki/Electromagnetic_fields#Mathematical_description

There are different mathematical ways of representing the electromagnetic field. The first one views the electric and magnetic fields as three-dimensional vector fields. These vector fields each have a value defined at every point of space and time and are thus often regarded as functions of the space and time coordinates. As such, they are often written as E(x, y, z, t) (electric field) and B(x, y, z, t) (magnetic field).

If only the electric field (E) is non-zero, and is constant in time, the field is said to be an electrostatic field. Similarly, if only the magnetic field (B) is non-zero and is constant in time, the field is said to be a magnetostatic field. However, if either the electric or magnetic field has a time-dependence, then both fields must be considered together as a coupled electromagnetic field using Maxwell's equations.[2]

With the advent of special relativity, physical laws became susceptible to the formalism of tensors. Maxwell's equations can be written in tensor form, generally viewed by physicists as a more elegant means of expressing physical laws.

 

[Bill_K]

Rather, it seems to show that while an "electromagnetic" effect is definitely real, it doesn't make much sense to say that something is fundamentally "electric" or "magnetic" because that distinction is observer-dependent.

In a limited sense it does. There are two invariant (frame independent) quantities that can be formed from the electromagnetic field, namely E·B and E² - B². Depending on whether the latter quantity is positive or negative, you can say that (at a particular point) an electromagnetic field is "mostly electric" or "mostly magnetic".